The present invention relates to liquid crystal displays used as a major component of projectors, projection TVs, etc. Particularly, this invention relates to an apparatus and a method of producing alignment layers to be used for liquid crystal displays and a liquid crystal display having alignment layers produced by the alignment-layer producing apparatus and method.
Active-matrix liquid crystal displays having TFTs, liquid crystal displays having a silicon wafer-to-glass plate stuck structure, etc., have been widely used for visual equipment such as projectors, projection TVs and head-mount displays, with increased production.
A known liquid crystal display 10 is shown in FIGS. 1 and 2. A glass substrate 2 is covered with a transparent conductive layer 1. Another glass substrate or a silicon IC substrate 4 has pixel electrodes (a displaying area) 3 thereon. A pair of alignment layers 5a and 5b are formed on the transparent conductive layer 1 and the glass substrate 4, respectively.
The glass substrates 2 and 4 are arranged as facing each other with a gap (cell gap). The cell gap is filled with a liquid crystal 6 through a fill-hole 9. The glass substrates 3 and 4 are then stuck each other via the liquid crystal 6 with a sealant adhesive 7 through the fill-hole 9 which will be sealed later. The sealant adhesive 7 is a mixture of spacers 7 and an adhesive (not shown) which define the cell gap. The glass substrate 2 is covered with an anti-reflective layer 8.
The alignment layers 5a and 5b are formed, for example, with a parallel alignment procedure in which an organic polymer such as polyimide is subjected to coating, for example, spin coating or offset printing, followed by baking and rubbing.
The parallel alignment procedure, however, has a lot of steps from polyimide printing to cleaning after rubbing. Moreover, rubbing could generate dust. It is further difficult through this procedure to attain high alignment properties (pretilt angle controllability) required for a desired displaying characteristics.
Application of the known liquid crystal display 10 to projectors and projection TVs requires high contrast ratio.
Another method of forming the alignment layers 5a and 5b for high contrast ratio is, for example, an oblique evaporation procedure with electron-beam deposition to form a metallic oxide layer of oxide silicon (SiO or SiO2) on the substrate from an oblique direction. This method requires no rubbing procedures and achieves high alignment properties and also high contrast ratio especially in vertical alignment system.
The oblique perpendicular alignment procedure is explained in detail with reference to FIG. 3.
Shown in FIG. 3 is an electron-beam deposition apparatus 20 equipped with an electron-gun unit U having a crucible 11 and an electron gun 19 with a filament 18. Oxide silicon 12 is contained in the crucible 11, as an evaporation source. The oxide silicon 12 is irradiated with electron beams 21 from the electron gun 19, as indicated by an arrow, so that it is heated and evaporated from the crucible 11. The evaporated particles of the oxide silicon 12 are dispersed upwards and obliquely deposited on the glass substrate 2 at an evaporation angle xcex8 from the direction of normal line on the substrate surface, thus forming an alignment layer of the oxide silicon 12 thereon. The crucible 11 is usually opened in a (vertical) direction 17 of the normal line on a base 16 of the apparatus 20. This direction of crucible""s opening is called the direction of the electron-gun unit U in the following disclosure.
This oblique evaporation utilizes anisotropic properties of the oxide silicon 12. Deposition (layer deposition) on the glass substrate 2 from an oblique direction provides an oblique thin layer with obliquely aligned long bar-like liquid-crystal molecules.
FIG. 4 illustrates oxide silicon 14a to 14n obliquely deposited on the glass substrate 2 and liquid-crystal molecules 15a to 15n aligned over the oxide silicon 14a to 14n. An angle xcex1 is a pretilt angle, and an angle xcex3 is an angle of layer deposition for the oxide-silicon alignment layer as disclosed later.
These methods are disclosed, for example, in Japanese Unexamined Patent Publication Nos. 5-257146, 6-186563 and 7-159788.
The electron-beam deposition for forming an alignment layer with the oxide silicon 12 as explained above has to meet crucial requirements for an oblique evaporation angle xcex8. It is, however, difficult to meet such crucial requirements and causes problems when several liquid crystal displays 10 shown in FIGS. 1 and 2 are formed on a large-size glass substrate 2.
The location of the glass substrate 2 in the electron-beam deposition apparatus 20 shown in FIG. 3 varies as the size of the substrate 2 varies as illustrated in FIG. 5. The oblique evaporation angle xcex8 also varies such as xcex8a and xcex8b in FIG. 5 as the location of the glass substrate 2 varies. This causes variation in angle of layer deposition xcex3 for the oxide silicon 14a to 14n shown in FIG. 4, thus alignment of liquid crystals is not uniform. This results in variation in image quality for the liquid crystal display 10. In illustration of change in deposition angle xcex8 in FIG. 5, xe2x80x9cdxe2x80x9d is the distance from the center of the glass substrate 2 formed by oblique deposition to the substrate edge.
Moreover, twist angles xcex94"psgr" are generated as shown in FIG. 6 when the glass substrate 2 is formed as being large in the direction perpendicular to the direction in which thin layer-structure of the oxide silicon 14a to 14n grows, or as being large in the direction perpendicular to the planer direction of the substrate 2 for higher productivity as discussed above. The twist angles xcex94"psgr" also depend on the location of the glass substrate 2 in the electron-beam deposition apparatus 20, as shown in FIG. 3. These angles also cause variation in image quality for the liquid crystal display 10.
One solution to these problems requires a small glass substrate 2 or a big deposition chamber 13 (FIG. 3) in the electron-beam deposition apparatus 20 to have an enough distance (deposition distance) D from the evaporation source 12 to the glass substrate 2.
However, the smaller the glass substrate 2, the more it is difficult to install the substrate 2 in the deposition chamber 13 and adopt an automatic substrate-installation mechanism.
Therefore, such solution has to employ a batch system in which small glass substrates 2 are processed. This system, however, causes generation of dust from the substrates while they are being processed, which results in low yielding and also low image quality.
Moreover, such a batch system takes time for sequential procedures of heating the glass substrates 2, reaching a target vacuum, forming layers on each substrate, cooling the substrates and vacuum bending. The total production process time thus depends on these procedures.
Furthermore, the bigger the deposition chamber 13, the more expensive the price of the electron-beam deposition apparatus 20, and also the larger the volume of the chamber, thus causing longer vacuum-reaching time, heating time, etc., for low productivity.
A long deposition distance D in the deposition chamber 13 could be attained with an evaporation-angle direction component of evaporated particles of the oxide silicon 12 to the glass substrate 2 which is obtained by shifting the electron-gun unit U in the direction horizontal to the base 16 of the electron-beam deposition apparatus 20, which is disclosed in, for example, Japanese Unexamined Patent Publication 6-186563.
This method, however, causes variation in evaporation rate for the oxide silicon 12 in the direction of evaporation, or lower evaporation rate as the electron-beam gun unit is shifted more and more, which thus results in low production.
The electron-beam deposition explained above for forming alignment layers with the oxide silicon 12 requires a precise pretilt-angle control for higher contrast ratio.
However, optimum values for such a precise pretilt-angle control must be found for several factors, such as, oblique evaporation angle xcex8, vacuum in the deposition chamber, substrate temperature, and thickness in alignment layer. These optimum values are necessary for the fact that the properties of oxide silicon layers have not known exactly, which nevertheless directly affect the pretilt-angle control. In production of liquid crystal displays, the best production requirements for alignment-layer deposition should be decided in accordance with evaluation of sample liquid crystal displays on pretilt-angles or image quality. The evaluation of sample liquid crystal displays, however, takes a lot of days.
A purpose of the present invention is to provide an apparatus and a method of producing alignment layers to be used for liquid crystal displays, for which large glass substrates can be adopted, for high image quality and productivity.
Another purpose of the present invention is to provide a liquid crystal display having alignment layers produced by the alignment-layer producing apparatus and method.
The present invention provides a method of forming an alignment layer to be used for liquid crystal displays each having at least two substrates with liquid crystals sealed therebetween, the method comprising the steps of: heating the substrates placed on each of several substrate trays in a first load-lock chamber; irradiating at least one of the two substrates with evaporated film of oxide silicon (SiOx: 1.0xe2x89xa6xc3x97xe2x89xa62.0) by vacuum deposition at an angle in the range from 45xc2x0 to 60xc2x0 from a direction of a normal line on the substrate surface to form an alignment layer thereon while the substrate trays are being moved in a deposition chamber intermittently or sequentially; and cooling the substrate trays in a second load-lock chamber, thus producing substrates each formed the alignment layer thereon.
Moreover, the present invention provides an apparatus for forming an alignment layer to be used for liquid crystal displays each having at least two substrates with liquid crystals sealed therebetween, the apparatus comprising a deposition chamber for depositing an alignment layer of oxide silicon (SiOx: 1.0xc3x972.0) on at least one of the two substrates under a requirement 0xe2x89xa6xcex94xcex8xe2x89xa63xc2x0 in xcex94xcex8=tanxe2x88x921(d cos xcex8/(D+d sin xcex8)) in which xe2x80x9cdxe2x80x9d is a distance from the substrate center to the center of a substrate edge required for alignment-layer deposition and xe2x80x9cDxe2x80x9d is a distance from the substrate center to the center of an evaporation source containing the oxide silicon for alignment-layer deposition, and xcex8 is an angle formed between a direction in which a normal line extends on the substrate center and another direction in which evaporated particles of oxide silicon are deposited on the substrate center from the evaporation source.
Furthermore, the present invention provides a reflective liquid crystal display having liquid crystals sealed between a transparent substrate and a silicon substrate, and an alignment layer of oxide silicon (SiOx: 1.0xe2x89xa6xc3x97xe2x89xa62.0) formed on at least one of the substrates at an angle of layer deposition in the range from 3xc2x0 to 10xc2x0 for alignment of the liquid crystals.